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MS Access Locking Files (.ldb)

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by dcarmageddon

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Hello all, I'm trying to figure out how MS Access uses locking files to lock records in a shared database. The following description is from Microsoft's introduction to .ldb files:
"The .ldb file is used to determine which records are locked in a shared database and by whom." "The .ldb file contents,
For each person who opens a shared database, the Jet database engine writes an entry in the .ldb file of the database. The size of each .ldb entry is 64 bytes. The first 32 bytes contain the computer name (such as JohnDoe). The second 32 bytes contain the security name (such as Admin). The maximum number of concurrent users that the Jet database engine supports is 255. Therefore, the .ldb file size is never larger than 16 kilobytes."
My question is, how does the Jet engine know which records are locked given that the information stored in the .ldb file consists of computer name and security name?

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by shellbot

The .LDB file includes information about the user, his computer name, and the records the user has open. As other users open the back-end MDB, their copies of Jet consult the .LDB file to determine which records are being edited.

http://my.advisor.com/articles.nsf/aid/13043

Good info article here about lock files.

by dcarmageddon

Thanks for that Shellbot. The article link you posted has the following comment at the bottom and is what I was looking for;

"Part of this is incorrect. The LDB does not contain the records that are being edited. The locking file is a 256 element array, with 32 character for the machine name and 32 characters for the user name. That's it. It will never grow larger then 16K. JET does not consult this file when looking for locks being held. Locks for an Access MDB are virtualized in the OS/NOS and placed on the LDB file. They are never physically written to disk."

-- Jim Dettman
Online Computer Services of WNY, Inc.
USA
05/31/2006 08:17 AM

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